WR25F 03 Bog on Idle Gone, Thanks

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I just wanted to say thanks :worthy:for the info on thumper talk. My friend told me about TT when I bought my bike last October. The info here combined with the manual helped me solve the bog and stalling right at idle. It finally turned out to be selecting the correct leak jet (40 or 50).

First, my riding technique is casual beginner and I ride trails in the mountains. I am in my 40's and wanted to ride trails and up until 2002 only rode street bikes. I rode the 02 XT 225 for a year but it was increadibly weak compared to my friend's YZ250F. Last October, I made the jump to the 03 WR250F as my dealer had one on the floor on sale advertised as derestricted an rejetted. The altitude here is 5000ft and at that time we still had days of 80 degrees. That was the first time I saw one on the floor and it was a fluke because a previous buyer did not qualify for financing. With the info here I was able to confirm that they just cut the throttle stop rather than measuring it. So I ordered a YZ stop. I ride slow and am not used to reving engines at high rmp. So I my max throttle was around 1/3. If I twisted the throttle too quick it would stall. Stalling is tougher for me as I am also short making the bike easier to tip over. This was dangerous when going up a hill in 1st or 2nd.

The dealer parts and salesman said it was a common problem with the bike and good luck in solving it . The mechanic that did the jetting and derestricting no longer worked there. Plus, their suggestions to fix the bog were a joke (fuel screw, starter jet). I performed the grey wire mod and also put a GYT-R insert in the muffler. It was a much better power compromise between no insert to using stock baffle. I don't want all the noise when in the forest but still want power when I go to a local track with my son. A physical inspection determined that the jetting was still stock. Anyway, there was no effect of the grey wire mod on the bog. By this time, I rode the bike for about 3 weeks and had a good baseline for how it was running out of the shop and where I wanted it to be.

At that point, following the manual, I leaned the main jet and needle. The assumption is at our altitude bikes run richer. The dealer standard suggestion is one clip up and two main jets down for our altitude. This was close to the manual suggestion to try one clip lean and one jet lean. I used a 38 piolt jet, one clip leaner on the needle, and a 180 main jet. The bog was still there and temps were still around 70.

I was sure that the problem was with the accelerator pump and figured from the manual that leak jets would control the amount of fuel. The info on the DHCP and the other accerator pump mods conerned me. I even looked at the squirt confirmed that it wasn't hitting the slide but still suspected that on my 03 that the leak jet controls the amount of fuel. Posts here at the same time discovered that there were various diaphram sizes and by selecting the correct diaphram and leak jet you could control the amount and duration of the squirt.

Through trial and error, the week and a half delay between ordering each leak jet, I found that a 60 elminated the bog at 70 degrees but returned as the temp droped to the 60s. So I currently have a 40 leak jet. The bog reappears at 50 degrees and below but that is too cold for me to ride.

I also was checking and cleaning the spark plug. The bike started running hotter and the plug started getting white powder at 50 degrees. I went back to standard jetting (40 pilot, 186 main, and middle clip on the needle). I plan to put the 50 leak jet in. As the temperatures warm up again the bog should stay gone. The standard jetting was fine (tan plug) when I was riding it at 80 degrees. It was that the 90 leak jet was producing too small a squirt that made the bike stall when you crack the throttle.

By the way, the first day I had the 60 leak jet in (the one that finally elminated the bog down to 70 degrees), the bike was a whole new bike with much more push . It no longer stalled from giving it gas. I tried and tried to stall it by cracking the throttle and could not. It was great knowing I could take a hill or turn slow but if the power was needed I could crack it and the bike zooms out. I was able to lift the front wheel at times with throttle alone. That really scares me but there is noway to describe the feeling of power the bike has. Also fun to walk into the dealer (who did not know what a leak jet did) and say the bike is great now that I solved the bog (that you, dealer couldn't).

Sorry about the long rant, but thanks for all the information here. I probably would have lived with the bog rather than solving it. As temperatures increase again (less dense air resulting in richer fuel mixture), I will be able to make adjustments to keep it running great. The biggest surprise to me was that you really should check the jetting when you run the bike without the stock baffle. The added airflow leans the bike. In my case, it compensated for the altitude. Now, if the temperatures would just get back up to the 50's so I can ride again.

The derestriction and free mods release a lot of power. The suspension saved from an endo at least twice already.

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Great write up! A lot of people had input in solving the bog puzzle, and I'm sure they're all very happy to hear stories like yours. Hopefully it'll encourage others to give it a try. Thanks for the feedback.

ps: I love the suspension too. My old XR would bottom out all the time, but I can launch this thing off of a 5' creek bank and it just soaks it up.

pps: If you want even more power, go with the JD jetting kit. Best bang-for-the-buck I've spent on the bike. Way more effect than the PowerNow.

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I have an 03 also, a quick question for you...where exactly do you adjust the AP squirt? I know I should read thumperfaq's but It does not clearly state what to look for on the 03....do I adjust a screw behind the housing plate? Tell me what to look for..thanks and congrats on the fix.

EJ

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The leak jet changes still apply to the 2003 models. Apparently the 2003 carburetor was redesigned and as a result there is no place to drill the hole for the BK mod. As far as we know, no one has come up with a solution. At present, the leak jet changes and the P-38 aftermarket pump cover appear to be the best solutions for too long of an AP squirt duration. There is no current information regarding the HB/Doc mod on the 2003 models. However, it is known that the 2003 models still have the leak jet, so assuming your AP squirt is too short this mod should still apply.

Also from ThumperFaq:

Newer bikes (either 2001 and up or just 250Fs) have a leak jet that 'leaks' some of the squirt back into the bowl. As indicated above, the leak jet gives you the flexibility to adjust the pump beyond the limits of those without it. The AP is purposely built too strong so a smaller leak jet would send most of the fuel into the venturi and a larger leak jet would send less into the venturi (that is, more would leak back into the bowl). This allows adjustment from too much to too little (volume). Part numbers for available leak jets can be found in the Yamaha Part Numbers section. The leak jets are numbered according to the size of the hole. For example, a #90 has a 0.90 mm diameter opening, a #80 has a 0.80 mm opening, and so on. There was a Yamaha service bulletin in 2001 regarding the use of leak jets and AP diaphragms. The date of the Yamaha service bulletin is 8/24/01 and it is labeled: "Report Number: 01-002" "Models - YZ250~426F, WR250F~426F(All Years): Subject - Optional Accelerator Pump Diaphragms and Leak Jets." Most service departments should have it in a book on the shelf somewhere for those who are interested.

Procedure

1)Remove the rear fender, subframe, airbox, and airboot. I also take the bell of the carburetor. The bell is not removable on the 2003-2004 models.

4)Measure your AP squirt. Make sure the fuel bowl is full, and that the pump diaphragm is loaded with gas. The best way to do this is to ride the bike around the block before hand, cracking the throttle numerous times to make sure it is well primed. Look into the carburetor using a flashlight. You will see the brass jet just behind the throttle plate on the bottom of the throat and slightly to the right of the middle. Quickly whack the throttle from closed to wide open. You will see a small stream of gas in the bottom of the venturi shooting back towards the slide. This is the AP squirt. Now time the duration of the squirt.

You can use a stopwatch to measure the time but given the very short duration this is likely somewhat inaccurate.

Use a camcorder to record the squirt. Then replay the squirt frame by frame (30 frames/sec) and calculate the duration.

5) Drop the bowl on the carburetor (you don't have to pull the carburetor). In the bottom of the bowl, about 1/2 way from the center to the back, brake side is a tiny brass jet with a flat head screwdriver slot in it. Unscrew it and see what number it has on it. Bigger number jets give less AP squirt (more is wasted back into bowl). Smaller number jets give more AP squirt (less is wasted back into bowl).

6) The goal in adjusting the AP is to select enough squirt to get it past the low RPMs but not enough to outlast the low RPMs or create a too rich condition during the low RPMs. It will burble like a two stroke with the choke on if too much and just have low acceleration. It will cough, cut out, or die without bucking at all if too little. Experiment with different leak jet sizes, using the charts below as a starting point, until the bike runs the best and your AP squirt duration is in the desired range (~0.5-1 seconds, some say 0.4-0.8 seconds).